The art of well-watching

Now is the time to start looking for yellow-bellied sapsuckers here in the Smokies region. Of the various woodpecker species that occur here, the sapsucker is by far the most migratory. Some can be located in the higher elevations of our mountains from spring into late summer, but sapsuckers appear in this area primarily as fall and winter residents.

Look for a woodpecker displaying long white shoulder patches. No other woodpecker species in eastern North America displays an elongated patch of this sort on each shoulder. Male sapsuckers display red throats, whereas the throats of females are white. The yellowish undersides that give the bird its common name are often not seen except when it’s in flight. The sapsucker race that breeds in the higher elevations of the southern mountains (distinguished by some ornithologists as the “appalachiensis” race) tends to be smaller and darker than individuals that breed farther north. Sapsucker’s call notes are squeaky, often containing plaintive, catlike mews.

The most distinguishing features of a sapsucker’s lifecycle are, of course, the shallow holes (sap wells) it excavates in the bark of trees so as to feed on the liquid that flows into them. This curious bird creates intricate systems of these wells and maintains them on a daily basis. They will vigorously defend their wells from other birds, including other sapsuckers.

Various animals have been observed utilizing the wells to supplement their own food intake with either the sap itself or the insects attracted to it. For instance, ruby-throated hummingbirds appear to be very closely allied with sapsuckers, placing their nests near the wells and following the sapsuckers in their daily movements. Some ornithologists have speculated that the hummers may even time their migrations to coincide with that of sapsuckers.

Observing sapsuckers obviously involves paying attention to their sap wells. In early spring, they drill them into the inner vascular tissues (xylem) of a tree’s trunk that are at that time moving sap upward. After the trees leaf out in late spring — and on through the summer, fall, and winter months — they drill the wells into the outer vascular tissues (phloem) of the trunk. Phloem tissues can contain as much as 25 percent sugar during the summer and 5 percent sugar during the winter.

Now we get down to the nitty-gritty part of sap well watching. Xylem wells created in spring are made by drilling round holes that are arranged in short horizontal rows of 3 to 15 small holes. Phloem wells created in other seasons begin as lateral slits that are expanded up a given tree’s trunk so as to form a rectangle.

(Note: Sources for this column are the writer’s personal observations; Fred W. Alsop’s Birds of the Smokies (1991); and, especially, The Birds of North America Online.)